The present invention relates to coordinate measuring machines. More particularly, the present invention is a machine for measuring and inspecting parts to a high accuracy (e.s., thousandths of an inch) wherein the machine measures displacement from a reference point in cylindrical coordinates. Cylindrical coordinates are a radius and an angular displacement within a plane from a fixed point and a perpendicular distance from the plane.
The prior art includes a number of coordinate measuring machines for measuring in rectangular coordinates. For the most part, these machines are referred to as "bridge" machines, "horizontal probe" machines, or "vertical probe" machines. Although each will be discussed in some detail, all have the characteristic of requiring rather long precision ways and guides. Such long precision ways are relatively expensive to manufacture and assemble in that they require precision machining to close tolerances. Such precision ways and guides are therefore undesireable in that they add significant expense to the manufacturing process.
Vertically mounted probe coordinate measuring machines are shown in various patents such as U.S. Pat. No. 3,403,448 to W. F. Aller entitled Measuring Machine. Such machines have long horizontal ways that require precision machining and additionally require very precise bearing systems to support accurately a moveable carriage which traverses across the ways.
One type of horizontal arm measuring machine is shown in U.S. Pat. No. 3,279,079 to Schiller for Inspection Machine. In such a machine, a horizontal arm is mounted on roller bearings or similar anti-friction materials to move vertically along vertical ways.
Bridge-type measuring machines are also well known in the prior art and include a carriage extending across and above the entire measuring work table. The carriage is supported on each end by a vertical support column which moves along horizontal ways along two parallel sides of the work table. Such machines usually require precision ways and that the carriage be accurately and securely coupled to the columns to minimize skewing.
Other bridge-type machines have been designed which minimize the effects of skewing but require relatively complex machanical and electronic designs which are undesirable.
Examples of such bridge type measuring machines are shown in U.S. Pat. Nos. 3,749,501 and 3,840,993.
As an alternate to the precision ways, some prior art measuring machines include an air assist between the moveable members. While such air assists may reduce the need for precision rails, the air assists add considerable complexity and expense to the machine especially since mechanical bearings are still required. Additional parts, manufacturing techniques and a source of pressurized air are required. One such pressurized air assist system for a measuring machine is shown in U.S. Pat. No. 4,099,800 to Tuss et al.
Many coordinate measuring machines have inherent stress conditions which result from the variable position of the probe (or other measurement member.) These machines have static and dynamic imbalances which are undesirable in that they create measurement errors.
Accordingly, the prior art measuring machines have undesirable disadvantages and limitations.